Future diesel engines need to comply with nitrogen oxide (NOx) emission standards which are continually being reduced. The emission standards are aimed at reducing air pollution from exhaust gases in line with the public interest in environmental protection. Generally speaking, there are two techniques of reducing NOx emission. One is improving combustion by lowering the combustion temperature and the other is after treatment of exhaust gases. In the conventional engine after treatment of exhaust gases by means of a catalytic converter is the main technique used to reduce NOx. This technique, however, has demerits of durability of the converter or air/fuel ratio control system especially oxygen sensors as well as cost. For the larger engine, these demerits become more severe problems. Whereas the technique for lowering NOx through improvement of combustion has merit especially with regard to durability and thermal efficiency of the engine.
Exhaust gas recirculation (EGR) has been shown to reduce NOx emissions with smaller brake specific fuel consumption (BSFC) and exhaust smoke penalties. Exhaust gas recirculation lowers NOx by diluting the fresh charge air with exhaust gas which lowers peak combustion temperatures and thus, reduces NOx production.
A preferred method of EGR is to have the exhaust gas cooled before being mixed with the charge air. Previous means of providing cooled EGR include transferring exhaust gas from the exhaust system to the air inlet system using external engine plumbing, a pump, and a heat exchanger to cool the exhaust gas. The exhaust gas is transferred from the exhaust system before or after the turbocharger turbine and to the air intake system before or after the turbocharger compressor. The result being increased customer cost and a greater possibility of hardware failure due to an increased number of components and complexity.
Thus, what is needed is an apparatus to obtain cooled EGR without the external hardware by using the capabilities within an engine having electronically controlled unit intake and exhaust valves and fuel injectors.
The present invention is directed to overcome one or more of the problems as set forth above.